The directional valve shown in Fig. a can be employed either as a normally closed or normally open valve, which is pilot-operated from one side. When used as a normally close valve, compressed air is supplied from the main to port 1, and port 2, the outlet port, is connected through a channel in valve member 5 to port 3, which is connected to the atmosphere. The valve is operated when compressed pilot air is admitted into port 6. As plunger 7 is shifted downward by air pressure exerted on its piston, first rubber insert 8 shuts off the channel in valve member 5, disconnecting port 2 from the atmosphere. Upon further motion, rubber insert 4 of valve member 5 is pushed off its seat. At this, air from port 1 is admitted into port 2. When the pilot air is switched o and port 6 is connected to the atmosphere, plunger 7 with its piston and valve member 5 are returned by the action o springs to the positions shown in Fig. a. When used as a normally open valve, compressed air is supplied from the main to port 3, and port 1 is used for connection to the atmosphere. The principle of the valve when used as normally closed is shown schematically in Figs. b and c.
$3689$SHP,FC$